1. Field of the Invention
The invention generally relates to devices and methods for guide wires that are used generally in cardiovascular and endovascular procedures, more specifically in atherectomy and/or angioplasty procedures, to facilitate the placement of catheters for angioplasty procedures and/or rotating drive shafts for atherectomy procedures within the vasculature of patients.
2. Description of the Related Art
A variety of techniques and instruments have been developed for use in the removal and/or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational atherectomy procedures have become a common technique for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries. Most often the rotational atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patentcy of the opened artery. For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patentcy of the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience stent restenosis—i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patentcy of the artery.
Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a burr covered with an abrasive cutting material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 150,000-190,000 rpm) while it is advanced across the stenosis.
U.S. Pat. No. 5,314,438 (Shturman) discloses another atherectomy device having a drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged cutting head being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.
U.S. Pat. No. 6,494,890 (Shturman) discloses an atherectomy device having a drive shaft with an enlarged eccentric section, wherein at least a segment of this enlarged section is covered with an abrasive material. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. The device is capable of opening an artery to a diameter that is larger than the resting diameter of the enlarged eccentric section due, in part, to the orbital rotational motion during high speed operation. Since the enlarged eccentric section comprises drive shaft wires that are not bound together, the enlarged eccentric section of the drive shaft may flex during placement within the stenosis or during high speed operation.
Typically a steerable guide wire is prepositioned within the lumen of the artery to a position at a point typically beyond or distal the obstruction, thus the guide wire must cross the occluded lesion. The atherectomy drive shaft may then be slid forward or distally along and over the prepositioned guide wire until the drive shaft, more particularly the abrasive surface of the drive shaft, is positioned adjacent or otherwise proximal the obstruction. The guide wire is thus pre-positioned prior to advancement of the typically less flexible and less steerable atherectomy drive shaft to facilitate advancement and positioning of the drive shaft at or adjacent the obstruction.
As discussed above, the atherectomy may be followed by an angioplasty procedure, a therapeutic medical procedure in which a catheter or the like is inserted into a blood vessel to increase blood flow as a safer, less expensive alternative to by-pass surgery. Typically, as with the atherectomy drive shaft discussed above, a steerable guide wire passes through the catheter and is able to move independently of the catheter. The guide wire is moved into position at a point typically beyond or distal the obstruction. The catheter is then slid forward or distally along and over the guide wire until the catheter is positioned adjacent or otherwise proximal the obstruction. The guide wire is thus pre-positioned prior to advancement of the catheter to facilitate advancement and positioning of the catheter at or adjacent the obstruction.
Several forms of guide wires for use in atherectomy drive shaft device and/or catheter placement are known. The simplest form of guide wire comprises a preferred diameter of between about 0.20-1.0 mm. The distal end of the known guide wire may comprise a bent tip that may be oriented to guide the wire along a vascular path. These types of guide wires may be difficult to steer through a tortuous vasculature and may encounter frictional difficulties along the lumen.
Other known guide wires comprise a flexible sheath or coating fused or heat shrunk to the guide wire to facilitate movement through the lumen. Coated guide wires do not allow the guide wire to comprise a longer taper section on the tip while still retaining the necessary columnar strength and flexibility required to move through the vasculature and ultimately through the obstruction. These guide wires may also be undesirable in that the sheath or coating cannot be removed once the guide wire is in position. The fused or coated sheath also increases the diameter of the guide wire which, in turn, requires a larger inner diameter and associated outer diameter for the device sliding over the guide wire.
Guide wires used to facilitate placement of devices to open occluded lesions must balance flexibility, steerability and outer diameter parameters with columnar strength. Insufficient columnar strength results in guide wires that have a tendency to buckle under axial compression during the insertion procedure, most typically while crossing the occlusion.
It is desirable to keep the diameter of the system itself, including the guide wire, as small as possible while retaining the required functionality. The guide wire must have sufficient flexibility while retaining steerability and columnar strength to allow crossing of occluded lesions. The present invention addresses these needs.